(1) Field of the Invention
The present invention relates to a highly acoustical auto ceiling panel and its manufacturing process.
(2) Description of the Prior Art
The conventional auto ceiling panel is a three-layer structure which represents a metal lath attached on both sides with polyethylene foams having isolated bubbles by thermal fusion; or a four-layer structure which represents a metal lath sandwiched between a vinyl chloride sheet-coated polyethylene foam and another polyethylene foam.
In such luminated structures (of three layers or four layers), the heat insulating effect and the safety to the human body may be fully assured, but on account of the bubbles in the polyethylene foam being isolated, the effect of absorbing the interior noise is not fully assured.
It has been known that a good effect of absorbing the sound will be secured when the auto ceiling panel is provided with through holes. Provision of such through holes in such a three-layer or four-layer panel will be hindered by the presence of a metal lath between polyethylene foams; and after lamination of these foams, it will be difficult to bore the through holes.
For these reasons it is the present practice to bore through holes separately in each polyethylene foam and thereafter laminate each foam on both sides of the metal lath, but even in this practice it is difficult to make lamination with the same pattern between top and bottom with the result that a very few through holes running through both polyethylene foams are obtained and thus the sound-absorbing effect is not so good for all the trouble of working.